Add chibicc

This program popped up on Hacker News recently. It's the only modern
compiler I've ever seen that doesn't have dependencies and is easily
modified. So I added all of the missing GNU extensions I like to use
which means it might be possible soon to build on non-Linux and have
third party not vendor gcc binaries.

libc/stdio/g_stdout.c

@@ -27,7 +27,7 @@ STATIC_YOINK("_init_g_stdout");
 
 FILE *stdout;
 hidden FILE g_stdout;
-hidden unsigned char g_stdout_buf[BUFSIZ] aligned(PAGESIZE);
+hidden unsigned char g_stdout_buf[BUFSIZ] forcealign(PAGESIZE);
 
 static textstartup void _init_g_stdout2() {
   struct FILE *sf;